Macrocyclic Trinuclear Nickel Phenoxyimine Catalysts for High-Temperature Polymerization of Ethylene and Isospecific Polymerization of Propylene

A series of macrocyclic
multinucleating phenoxyimine ligands and
the corresponding neutral binuclear (2-Ni2) and trinuclear (3-Ni3) nickel catalysts have been efficiently synthesized. The trinuclear
nickel complex 3-Ni3 showed high
activity, high thermal stability, and slow chain transfer in ethylene
polymerization, thus producing polyethylene with high molecular weight
and low branch density. Highly regiospecific and isospecific polymerization
of propylene was also achieved with 3-Ni3, generating regioregular and highly isotactic propylene with
high Tm and crystallinity. This is the
first example of regio- and stereocontrolled propylene polymerization
promoted by nickel phenoxyimine catalysts. Statistical analysis suggested
selective 1,2-insertion and enantiomorphic site control mechanism
in the chain propagation step, likely caused by the unique steric
effect of macrocyclic ligands and the potential cooperative effect.